I just installed Windows 8.1 on my laptop and tried out the new scaling for the desktop when using multiple monitors with different DPIs.

It is improved and more usable now, but still has issues unfortunately.

I've played with it for a few minutes and this is what I've learned

UI elements will now be the right physical size on any screen regardless of the DPI

UI elements are still actually rendered at one scale factor, the scale factor of the primary display

UI is stretched or shrunk to be the right size on any display not using the current scale factor

Scale factor still requires log out and log in to change

The common scenario that people will be having this problem with is using all the new high DPI laptops and tablets with external standard DPI monitors.

In Windows 8 if you set scaling to 125% or 150% to be the right physical size on the laptop everything will be way too big on the external screen when plugged in.

Now everything will be the right physical size but this is done by stretching or shrinking the pixels, causing re-sizing distortion and loss of crispness. But you will at least be able to use screens with different DPIs without one being too large or too small.

So lets say you're using your ATIV Smart PC Pro, Surface Pro, or other high DPI device undocked with 150% scaling on the screen. This works all great. Now plug in your external monitor.

On Windows 8 everything is HUGE

On Windows 8.1 everything is the right physical size but now blurry because they were shrunk down to 2/3 their previous size, a non-integer amount causing blurriness

Now lets say you'll be using the external monitor for some time and want the graphics to be optimized for it

On Windows 8 you had to go to the scaling options, change to 100%, log out, and log back in. This causes the external monitor to operate optimally but now everything is tiny on the built-in screen. Tough luck.

On Windows 8.1 you just need to log out and back in. No need to change any settings. The external monitor is now operating optimally. The internal screen on the device still shows everything the correct size, but is now stretching everything 150%, causing them to be blurry.

There are a few exceptions.

IE11 will always render at the current scale factor, no matter which monitor it is on. You can zoom the pages in and out.

Taskbar always renders at current scale factor

Task manager will always render at current scale factor

Time to unplug external monitor and go mobile.

On Windows 8 you had to go into the scaling options, set to 150%, log out, log in. If you do not do this, everything will continue to render at 100% and be too small.

On Windows 8.1 you just have to log out and back in. If you do not do this, everything will render at the right physical size but be stretched by 150% causing them to be blurry.

Metro works perfectly and did in Windows 8.0

Note: This was tested using a laptop with standard DPI, an external screen with standard DPI set to 125%. I no longer have a high DPI ATIV Smart PC Pro but was still interested in this. If anyone finds anything wrong please reply.

Glad to see this post. I wasn't sure if it was just me or not. I really do hope that they fix having to log out / back in to fix the large elements when plugging in an external monitor.

You mean to optimize them for the primary display? In 8.1 preview they're the right size, but I think the windows desktop display subsystem doesn't support having programs render at two different DPIs simultaneously. Programs weren't designed to do so. I think they're going to have to do some major work to make it so and even then every program will have to be updated to work correctly. They could probably make programs render at the DPI of the monitor they were opened on, but dragging a running program from one monitor to another monitor with a different DPI is probably impossible without the programs being updated.

Talking about when I log in on the tablet without an external monitor connected, then connect the external monitor. The taskbar and all apps are the appropriate size, but all the text and icons are scaled at the original monitor's scale.

Talking about when I log in on the tablet without an external monitor connected, then connect the external monitor. The taskbar and all apps are the appropriate size, but all the text and icons are scaled at the original monitor's scale.

Is the external monitor set as the default monitor? If it is default and connected when you log in then Windows will render at that DPI, and stretch things out to be the right size on the tablet's screen, but will be blurry on the tablet. Like I said, I think this is due to how the desktop graphics system works. It was never designed with simultaneous different-DPI displays in mind.

Which is exactly what I am hoping they fix before the release. It shouldn't require a log out to fix everything on connect/disconnect.

It shouldn't, but don't hope for any better for 8.1. Maybe 8.2

Desktop is going to take a major back-end overhaul to work nicely.

I'm curious, how does Apple handle this? Do unmodified old programs work correctly? I've searched Google quite a bit and no one seems to have posted a detailed explanation of how this works on retina macbooks.

The most information I could dig up is it seems that Apple sometimes renders things at insanely high resolutions and then scales them down. They seem to still look decent like that.